1. Field of the Invention
This invention relates generally to methods of providing input to a touchpad. Specifically, the invention relates to a method of reducing latency that a touchpad or touch-sensitive screen might experience when executing single and multi-touch gestures.
2. Description of Related Art
Electronic appliances are now performing more and more functions in all parts of our daily lives. There is a need for more and better ways to use and control both portable and non-portable electronic appliances.
The ubiquitous touchpad and touchscreen are being integrated into an ever increasing array of products because touch is a preferred method of interaction with electronic appliances. A short list of portable electronic appliances demonstrates that users are already benefiting from using a touch sensitive surface as a means of providing user input. These portable electronic appliances include, but should not be considered limited to, music players, DVD players, video file players, personal digital assistants (PDAs), digital cameras and camcorders, mobile telephones, laptop and notebook computers, global positioning satellite (GPS) devices and many others. Even stationary electronic appliances such as desktop computers can take advantage of an improved system and method of providing input to a touchpad (hereinafter the term “touchpad” will also refer to a “touchscreen”) that provides greater functionality to the user.
One of the main problems that many portable and non-portable electronic appliances have is that their physical dimensions limit the number of ways in which interacting with the appliances is possible. There is typically a very limited amount of space that is available for an interface when portability is an important feature. For example, mobile telephones often referred to as smart phones are now providing the functions of a telephone and a personal digital assistant (PDA). Typically, PDAs require a significant amount of surface area for input and a display screen in order to be practical.
A key aspect of using any small electronic appliance, and especially a device that includes a display, is reducing frustration when dealing with the device. If interaction with the device is difficult, then it won't be used. Thus, new systems and methods of interacting with touchpads are being created to improve the user experience.
A relatively new method of user input using a touchpad is the use of multi-touch gestures. Specifically, a user uses multiple pointing objects, such as a finger and a thumb, to perform a gesture on or near the touchpad. Different objects and more objects can also be used. The gesture is then interpreted as a command for controlling some function that can be performed on or by the electronic appliance. For example, a pinching motion with a finger and thumb can be interpreted as a gesture command for controlling a zoom function on a display screen.
Before describing the new method for reducing latency when using a touchpad that can accept multi-touch input, it is useful to describe one embodiment of touchpad technology that can be used in the present invention. Specifically, the capacitance-sensitive touchpad technology of CIRQUE® Corporation can be used to implement the present invention. The CIRQUE® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated in FIG. 1. The touchpad can be implemented using an opaque surface or using a transparent surface. Thus, the touchpad can be operated as a conventional touchpad or as a touch sensitive surface on a display screen, and thus as a touch screen.
In this touchpad technology of CIRQUE® Corporation, a grid of row and column electrodes is used to define the touch-sensitive area of the touchpad. Typically, the touchpad is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these row and column electrodes is a single sense electrode. All position measurements are made through the sense electrode. However, the row and column electrodes can also act as the sense electrode, so the important aspect is that at least one electrode is driving a signal, and another electrode is used for detection of a signal.
In more detail, FIG. 1 shows a capacitance sensitive touchpad 10 as taught by Cirque® Corporation includes a grid of row (12) and column (14) (or X and Y) electrodes in a touchpad electrode grid. All measurements of touchpad parameters are taken from a single sense electrode 16 also disposed on the touchpad electrode grid, and not from the X or Y electrodes 12, 14. No fixed reference point is used for measurements. Touchpad sensor control circuitry 20 generates signals from P,N generators 22, 24 that are sent directly to the X and Y electrodes 12, 14 in various patterns. Accordingly, there is a one-to-one correspondence between the number of electrodes on the touchpad electrode grid, and the number of drive pins on the touchpad sensor control circuitry 20.
The touchpad 10 does not depend upon an absolute capacitive measurement to determine the location of a finger (or other capacitive object) on the touchpad surface. The touchpad 10 measures an imbalance in electrical charge to the sense line 16. When no pointing object is on the touchpad 10, the touchpad sensor control circuitry 20 is in a balanced state, and there is no signal on the sense line 16. There may or may not be a capacitive charge on the electrodes 12, 14. In the methodology of CIRQUE® Corporation, that is irrelevant.
When a pointing device creates imbalance because of capacitive coupling, a change in capacitance occurs on the plurality of electrodes 12, 14 that comprise the touchpad electrode grid. What is measured is the change in capacitance, and not the absolute capacitance value on the electrodes 12, 14. The touchpad 10 determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line 16 to reestablish or regain balance on the sense line.
The touchpad 10 must make two complete measurement cycles for the X electrodes 12 and for the Y electrodes 14 (four complete measurements) in order to determine the position of a pointing object such as a finger. The steps are as follows for both the X 12 and the Y 14 electrodes:
First, a group of electrodes (say a select group of the X electrodes 12) are driven with a first signal from P, N generator 22 and a first measurement using mutual capacitance measurement device 26 is taken to determine the location of the largest signal. However, it is not possible from this one measurement to know whether the finger is on one side or the other of the closest electrode to the largest signal.
Next, shifting by one electrode to one side of the closest electrode, the group of electrodes is again driven with a signal. In other words, the electrode immediately to the one side of the group is added, while the electrode on the opposite side of the original group is no longer driven.
Third, the new group of electrodes is driven and a second measurement is taken.
Finally, using an equation that compares the magnitude of the two signals measured, the location of the finger is determined.
Accordingly, the touchpad 10 measures a change in capacitance in order to determine the location of a finger. All of this hardware and the methodology described above assume that the touchpad sensor control circuitry 20 is directly driving the electrodes 12, 14 of the touchpad 10. Thus, for a typical 12×16 electrode grid touchpad, there are a total of 28 pins (12+16=28) available from the touchpad sensor control circuitry 20 that are used to drive the electrodes 12, 14 of the electrode grid.
The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes on the same rows and columns, and other factors that are not material to the present invention.
Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes and a separate and single sense electrode, the sense electrode can also be the X or Y electrodes by using multiplexing. Either design will enable the present invention to function.
The underlying technology for the CIRQUE® Corporation touchpad is based on capacitive sensors. However, other touchpad technologies can also be used for the present invention. These other proximity-sensitive and touch-sensitive touchpad technologies include electromagnetic, inductive, pressure sensing, electrostatic, ultrasonic, optical, resistive membrane, semi-conductive membrane or other finger or stylus-responsive technology.
It would be an advantage over the prior art to provide a new method for using a touchpad that is capable of single and multi-touch gestures, wherein there is no latency in touchpad operation when either type of gesture is being executed.